Magnetic drive



E. B. ROMBERG MAGNETIC DRIVE Dec. 25, 1962 2 Sheets-Sheet 1 Filed Dec.8, 1958 OSCILLATOR 'l/IIIIII'IIII 'I'IIII III:

INVENTOR. EDGAR B. ROMBERG ATTORNEY Dec. 25, 1962 ROMBERG 3,070,024

MAGNETIC DRIVE Filed Dec. 8, 1958 2 Sheets-Sheet 2 l x a as 39 35 as 55as I 3 OSCILLATOR 44 3| FIG. 4

INVENTOR.

EDGAR B. ROMBERG United States Patent Gflflce 3,079,024 Patented Dec.25, 1962 359703124 MAGNETIC DRHVE Edgar B. Romberg, Whittier, Califassignor to North American Aviation, inc. File-ti Dec. 8, 195%, Ser. No.779,1116 9 Claims. (Cl. LS-53) This invention relates to magneticcircuits, and more particularly concerns apparatus forelectromagnetically driving a driven element with maximum efficiency.

Electromagnetic Solenoid devices are commonly arranged so that thelength of the air gap changes with motion of the armature. This resultsin a reluctance change and consequently provides a force which isproportional to the square of the displacement of the armature. Withsuch an arrangement, there are excessive forces during part of themotion of the armature which inherently requires more input power andmore core material and windings than is necessary to produce the forceachieved at those positions where the gap length is maximum.Furthermore, in the magnetic circuits of most solenoid devices, the areaof the air gap is generally relatively small as compared to the size ofthe core and windings whereby increased size, weight and cost arerequired.

In accordance with the present invention, there is provided a magneticcircuit in which the length of the air gap, or fiaps, may remain fixedwhile the area of the gap, or gaps, is caused to change directly witharmature motion. Thus, the reluctance of the magnetic circuit variesdirectly with the armature motion and a relatively constant magneticforce can be achieved. An armature is mounted for reciprocation withinan air gap formed between two magnetic pole faces so as to replace suchair gap with two smaller length gaps in series. In order to obtainmaximum driving force for a given size of parts, a plurality ofinterconnected armature elments are utilized to provide a plurality ofpairs of gaps in series whereby total gap area is substantiallyincreased. The several armature elements are magnetically isolated fromeach other in order to minimize binding of the armature elements withinthe gaps due to the flow of flux between different armature elements.

In one embodiment, there is provided a toroidal or annular magnetic corehaving an annular magnetic gap. An armature ring of discontinuousmagnetic material is mounted coaxially of the core for axial motionwithin the annular gap. Suitable means are provided to selectively orrepetitively energize the core. For use as a reciprocating pump, thismagnetic drive structure is provided with a piston secured to thearmature ring and having a diameter considerably smaller than thediameter of the armature ring whereby maximum force is obtainable with agiven amount of iron and copper in the core and its coil. The piston is,of course, operably mounted in a suitable fluid-containing chamber orcylinder and resiliently urged in a direction opposing the direction ofthe magnetic forces.

It is an object of this invention to provide a magnetic drive ofincreased efliciency.

A further object of the invention is to provide an improved fluid pump.

Another object of the invention is to provide a magnetic circuit ofmaximum gap area.

Still another object of the invention is to provide a magnetic circuitin which the reluctance will vary directly with relative motion of theparts.

A further object of the invention is to eliminate radial binding forcesfrom a magnetic circuit having an annular armature.

A still further object of the invention is to provide a magneticallydriven fluid pump in which the magnetic gap area is considerably greaterthan the piston area.

These and other objects will become apparent from the followingdescription taken in connection with the accompanying drawings in which:

FIG. 1 depicts a structure illustrating certain principles of theinvention;

FIG. 2 is a section on line 22 of FIG. 1;

FIG. 3 illustrates an arrangement for varying the linearity of thereluctance;

FIG. 4 shows a fluid pump constructed in accordance with the concepts ofthe invention;

And FIG. 5 is a second view of the armature of the pump of FIG. 4.

In the drawings, like reference characters refer to like parts.

Referring now to FIGS. 1 and 2, there is: shown a magnetic drivecomprising an electromagnet forming first and second pairs of opposingmutually-spaced magnetic pole faces 1%, 11 and 12, 13, provided bymagnetic cores 14, 15, which are of substantially C-shapedconfiguration. As illustrated, the cores 14, 15 may be suitably aflixedto a case or support 16. A pair of armature elements 17, 13 are mountedfor reciprocation between the pole face pairs 1%, 11 and 12, 13,respectively. The armature elements 17, 18 are rigidly or fixedlyinterconnected by an arm 19 which is positioned to abut a top wall 21)of the case 16 in the upper limiting position of the armature and toabut the surfaces 21, 22 of the cores 14, 15 in the lower limitingposition. The armatures 17, 18 are of any suitable low-reluctancemagnetic material while the arm 19 is formed of high reluctance or anon-magnetic material to minimize or prevent flux flow between thearmatures. The armature assembly 17, 18, 19 is resiliently urged to theupper limiting position thereof by any suitable means such as spring 25mounted to abut at its respective ends the arm 19 and the bottom wall ofcase 16.

Means are provided for repetitively energizing the cores 14, 15 -toprovide a fiux flow such as in the directions indicated by arrows 26, 27(or in directions opposite to those indicated) between the faces of eachpair of pole faces in substantially alined but in opposite directions.Specifically, a winding 28 is wound about the legs 29, 30 of cores 14,15 and connected to be cyclicly energized by some suitable source offluctuating electrical energy such as the oscillator 31. The oscilllator31, for example, may be a conventional 60-cycle supply. It will bereadily appreciated that a direct-current source may be utilized byproviding a normally closed switch arranged to be opened upon downwardmotion of the armature as is well known in the art.

It will be seen that the relatively long gap between pole faces 12, 13is replaced by a pair of gaps g and g in series each of which is of anunvarying length during reciprocal motion of the armature. Uponenergization of the coil 28, the force 7, tending to pull the armaturefurther down into the gap, is given by the expression direction ofarmature motion. The quantity is defined as where g is the total gaplength (g +g and A is the gap area which is the product of gap width wand the distance x of penetration of the armature into the gap.Substitution of Equation 2 into Equation 1 yields where K is a constantincluding the term .41rw. Examination of Equation 3 indicates that themagnetic force is constant for a constant gap length.

It is desirable in the arrangement of FIGS. 1 and 2 that each armatureelement be centered within the long gap formed by the cooperating polefaces so that the series gaps g and g are equal. A difference in lengthof gaps g and g in the illustrated arrangement utilizing a plurality ofarmature element-s, would cause increased lateral forces tending todisplace the armature in one direction or the other toward an adjacentmagnetic pole face. For example, if the armature 18 were displacedtoward the right in FIG. .1, flux would flow across gap g from pole face13 to armature 18, thence through the arm 19 (if it were low magneticreluctance) to armature element 17 and across the narrow gap to the poleface 11 of core 14. Thus, the lateral radial forces would beinordinately increased by the use of plural armature elements if theconnecting arm 19 were not of high reluctance material.

It will be seen that the arrangement illustrated in FIGS. 1 and 2provides a force which does not vary during the length of the stroke ofthe armature and at the same time provides a substantial increase in gaparea by providing plural armature elements each with two working gaps gand g It will be readily appreciated that additional symmetricallydisposed armature elements may be provided for cooperation withadditional pairs of magnetic pole faces. Such an arrangement isillustrated in FIGS. 4 and which show the concept of this invention asapplied to a reciprocating fluid pump. Mounted within a completelyclosed, sealed pump housing 35 is a toroidal or annular core 36 which isof substantially C-shaped cross section. A toroidal coil 37 is woundabout the inner annular leg 38 of the core. The coil is connected to anoscillator 31 via leads 39 extending through suitable apertures in thehousing 35 and the core 36. Coaxially fixed within the core 36 iscylinder sleeve 40 in which is reciprocably mounted an axially boredpiston 41. The fluid chamber, or cylinder, is provided with aunidirectional inlet valve comprising ball 42 and valve seat 43 forcommunication with an inlet port 44 formed in the housing 35. An outletport 46, formed in the housing 35, is in fluid communication with theinterior of the cylinder which receives fluid upon the downward (intake)stroke of the piston through a unidirectional valve comprising a ball 47and a valve seat 48 formed within the piston 41. Suitable means such asthe 'O-ring .9 is provided to seal the inlet port 44 from the cylinderpressure chamber.

The piston is formed with circumferential flange 50 to which is fixedlysecured, as by swaging, an annular armature ring 51 of discontinuousmagnetic material. The magnetic discontinuities of the armature ring 51are provided by a plurality of radial slots 52 which may, if desired,extend completely to the piston flange 50. Resilient means which may bea single annular spring, or the illustrated plurality of springs 54, aremounted in apertures 55, bored in the core 36 to abut the surface of thearmature 51. A plurality of apertures 56, 57 are formed in the pistonflange 5t and the armature ring 51 in order to decrease the viscous dragon the piston and armature.

It will be seen that the annular armature 51 in effect comprises aplurality of armature elements arranged in diametrically-opposed pairs60-61, 62-63, etc., each of which pairs is substantially similar to thesingle armature element pair 17-48 of FIGS. 1 and 2. The slots 52, whichprovide a' high reluctance magnetic path between the several armatureelements, are wedge shaped as indicated at 65, in order to equalize gapwidth w of the gaps g and g on the radially inner and outer sides of theindividual armature elements. It has been found that it is not necessaryto extend the high reluctance slots 52 the full distance to the centerof the armature since it is merely necessary to minimize thecross-sectional area of the flux path 66 between the respective armatureelements. The thickness of the portion 66 of the armature ring 51 ismade small enough so as to effect saturation thereof when the coil isenergized.

For a pump such as illustrated in FIG. 4, which is particularly adaptedto provide pressurized fluid to aircraft carried instruments such asgyroscopes and distance meters, the energization of the coil may be mostconveniently effected by utilizing a synchronized bistable multivibratoror flip-flop as the oscillator 31. This is desirable by reason of thefact that the conventional aircraft power supply of 400 cps. is of toohigh a frequency for optimum operation of such a pump. It has been foundconvenient to operate a pump such as that illustrated in FIG. 4 having ahousing diameter on the order of 1 inch at a frequency of about 10cycles per second by the use of a flip-flop which energizes the solenoidcoil for a period such as 20 per-cent of the cycle. The 20 percentenergizing period of the 10 c.p.s. frequency is chosen so as to be justlong enough to pull the armature fully down into the annular gap of thecore to complete the intake stroke. During the following percent of eachcycle, the springs return the armature and piston to their upperlimiting position (in abutment with the top wall of the casing 35) forthe pumping stroke. A pump such as illustrated in FIG. 4, providing anoutput pressure of 20 to 40 pounds per square inch,

. has operated over five-thousand hours without appreciable wear. Suchlong life may be attributed largely to the minimization of the radialforces which are largely eliminated by the discontinuity of the annulararmature.

On the intake stroke, the springs are compressed. The force exertedthereby increases to some extent. Consequently, for the highestefliciency, the magnetic forces acting against the spring forces shouldincrease in proportion. Thus, each of the armature elements 69 through6'3 may be tapered as illustrated in FIG. 3 so that the gap lengths gand g will decrease during the intake stroke of the pump in directproportion to the increase in spring force. With such an arrangement,the magnetic force can at all times be made equal to or a small fixedamount greater than the spring forces for all armature positions.

It will be readily appreciated that while a specific embodiment of theinvention has been illustrated as providing the reciprocal magneticdrive for a miniaturized reciprocating fluid pump of maximum efliciency,the principles of the disclosed invention may equally well be practicedin any arrangement wherein a constant driving force is required toprovide a linear motion of a driven element. The variety of uses of thedisclosed reciprocating magnetic motor will be readily apparent to thoseskilled in the art.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample only and is not to be taken by way of limitation, the spirit andscope of this invention being limited only by the terms of the appendedclaims.

I claim:

1. A pump comprising a casing having inlet and outlet ports, a magneticcore mounted in said casing and spaced from one side thereof, said corehaving an annular magnetic gap having inner and outer annular faces, acoil on said core, said core having an axial bore providing a pumpingcylinder, valve means for providing communication between said cylinderand said ports, a piston slidably mounted in said cylinder, an armaturefixed to said piston and extending in the space between said core andeasing, said armature having a peripheral flanged projectingsubstantially normal to the armature body and into said gap to providean annular magnetic armature having inner and outer faces respectivelyadjacent said inner and outer gap faces, said armature body and flangehaving a number of slots extending substantially radially thereof tominimize flow of magnetic flux circumferentially of said armature.

2. The structure of claim 1 wherein said slots are outwardly divergentto equalize the circumferential length of inner and outer portions ofsaid flange between adjacent slots.

3. An annular magnetic core having an annular magnetic gap, an armaturehaving a disc portion coaxial with said core and mounted for axialreciprocation relative thereto, said disc portion fixedly carrying anannular magnetic armature flange of low reluctance magnetic materialpositioned to reciprocate within said annular gap, said disc portion andarmature flange having a plurality of radially extending slots providinghigh reluctance to circumferential flow of flux around said armature,and a coil on said core, the sides of each said slot mutually divergingfrom inner to outer surfaces of said flange so as to equalize said innerand outer gap widths.

4. An annular magnetic core having an axial bore and an annular magneticgap, said gap having mutually facing inner and outer pole faces, a coilon said core, a reciprocable member slidably mounted in said core bore,an armature having a disc portion fixed to said member and extendingradially outwardly to said gap, said armature having a peripheral flangeof low reluctance magnetic material projecting substantially normal tothe disc portion thereof to and within said gap, said flange havinginner and outer surfaces respectively adjacent said inner and outer polefaces to provide equal-length inner and outer magnetic gaps, said flangehaving a plurality of slots each diverging outwardly from inner to outersurfaces thereof so as to decrease the difference in area between saidinner and outer magnetic gaps.

5. The structure of claim 4 wherein said flange is tapered in thedirection of its projection so as to effect decrease of gap length uponmotion of said flange into said core.

6. A magnetic core comprising an annular magnetic gap having inner andouter annular faces, a coil on said core, an armature mounted forreciprocation relative to said gap faces in a direction substantiallyparallel to said faces, said armature having a central web portion, aperipheral flange of low reluctance magnetic material projectingsubstantially normal to the web portion into said gap to provide anannular magnetic armature portion having inner and outer facesrespectively adjacent said inner and outer gap faces, said armaturehaving a number of slots extending substantially radially thereof tominimize flow of magnetic flux circumferentially of said armature.

7. A magnetic drive comprising electromagnetic means forming first andsecond opposing mutually spaced magnetic pole faces of endlessconfiguration, means for energizing said electromagnetic means toprovide flux flow between said faces in a direction normal thereto, aplurality of mutually spaced armature elements of low reluctancemagnetic material arranged in diametrically opposed pairs, said elementsbeing fixedly related to each other and being mounted for reciprocationbetween and relative to said pole faces in a direction substantiallyparallel to said faces and normal to said direction of flux flow.

8. A magnet core having inner and outer pole faces forming an endlessmagnetic gap providing a flux flow in a direction extending between saidfaces, a coil on the magnet core, a segmented armature mounted forreciprocation relative to said magnet in a direction substantiallyparallel to said faces and normal to said direction of flux flow, saidarmature having segments of low reluctance magnetic material extendinginto said gap so as to vary magnetic gap area between said pole facesand the segments as the armature reciprocates, each said segment havinga cross-section which varies in the direction of said reciprocation soas to efifect some decrease in gap length, upon reciprocation, duesolely to such varying cross-section.

9. An annular magnetic core having an axial bore and an annular magneticgap, said gap having mutually facing inner and outer pole faces, a coilon said core, a reciprocable member slidably mounted in said core, anarmature having a web portion fixed to said member and extendingradially outwardly to said gap, said armature having a peripheral flangeof low reluctance magnetic material projecting substantially normal tosaid web portion to and within said gap, said flange having inner andouter surfaces respectively adjacent said inner and outer pole faces toprovide inner and outer magnetic gaps, said flange having a plurality ofslots and being smaller at its projecting end portion so as to decreasethe gap lengths upon motion of said flange into said core.

References Cited in the file of this patent UNITED STATES PATENTS1,822,242 Schongut Sept. 8, 1931 2,274,775 Cox Mar. 3, 1942 2,630,760Ryba Mar. 10, 1953 2,853,229 Dolz S ept. 23, 1958 2,872,101 Ryba Feb. 3,1959 2,926,615 Oofiey Mar. 1, 1960 FOREIGN PATENTS 409,843 Italy Mar. 5,1945 623,449 Great Britain May 18, 1949 830,433 France May 16, 1938842,073 France Feb. 20, 1939

